cmp_compares — Mathlib

English

For every a,b ∈ ONote with NF, the relation (cmp a b).Compares a b holds, i.e., the comparator correctly determines the ordering of a and b.

Русский

Для любых a, b ∈ ONote с NF выполняется, что (cmp a b).Compares a b, то есть компаратор корректно определяет порядок между a и b.

LaTeX

$$$\forall a,b : ONote\,[a.NF][b.NF],\; (cmp\; a\; b).Compares\; a\; b$$$

Lean4

theorem cmp_compares : ∀ (a b : ONote) [NF a] [NF b], (cmp a b).Compares a b
  | 0, 0, _, _ => rfl
  | oadd _ _ _, 0, _, _ => oadd_pos _ _ _
  | 0, oadd _ _ _, _, _ => oadd_pos _ _ _
  | o₁@(oadd e₁ n₁ a₁), o₂@(oadd e₂ n₂ a₂), h₁, h₂ => by -- TODO: golf

    rw [cmp]
    have IHe := @cmp_compares _ _ h₁.fst h₂.fst
    simp only [Ordering.Compares, gt_iff_lt] at IHe; revert IHe
    cases cmp e₁ e₂
    case lt => intro IHe; exact oadd_lt_oadd_1 h₁ IHe
    case gt => intro IHe; exact oadd_lt_oadd_1 h₂ IHe
    case eq =>
      intro IHe; dsimp at IHe; subst IHe
      unfold _root_.cmp; cases nh : cmpUsing (· < ·) (n₁ : ℕ) n₂ <;> rw [cmpUsing, ite_eq_iff, not_lt] at nh
      case lt =>
        rcases nh with nh | nh
        · exact oadd_lt_oadd_2 h₁ nh.left
        · rw [ite_eq_iff] at nh; rcases nh.right with nh | nh <;> cases nh <;> contradiction
      case gt =>
        rcases nh with nh | nh
        · cases nh; contradiction
        · obtain ⟨_, nh⟩ := nh
          rw [ite_eq_iff] at nh; rcases nh with nh | nh
          · exact oadd_lt_oadd_2 h₂ nh.left
          · cases nh; contradiction
      rcases nh with nh | nh
      · cases nh; contradiction
      obtain ⟨nhl, nhr⟩ := nh
      rw [ite_eq_iff] at nhr
      rcases nhr with nhr | nhr
      · cases nhr; contradiction
      obtain rfl := Subtype.eq (nhl.eq_of_not_lt nhr.1)
      have IHa := @cmp_compares _ _ h₁.snd h₂.snd
      revert IHa; cases cmp a₁ a₂ <;> intro IHa <;> dsimp at IHa
      case lt => exact oadd_lt_oadd_3 IHa
      case gt => exact oadd_lt_oadd_3 IHa
      subst IHa; exact rfl

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